Prenatal Screening

During the course of your prenatal care you will be offered a screening test for birth defects. This test is offered across the country to women who are 15-20 weeks along in their pregnancies. Its purpose is to determine if you are at increased risk for having a child with a Neural Tube Defect (a malformation of the spine or skull that can cause paralysis or which can be fatal) or with Down's Syndrome (a genetic defect causing mental retardation and other physical problems).

The test you will be offered will require that you have blood drawn and sent to the laboratory. It will be analyzed for three substances: alphafetoprotein (a protein produced by the growing fetus which shows up in the amniotic fluid and can be detected in small levels in your blood), human chorionic gonadotropin (HCG), (a hormone made by the placenta), and unconjugated estradiol (a substance produced by the fetus and placenta). Based on the levels of these substances found in your blood, you may be found at increased risk for a Neural Tube Defect or for Down's Syndrome.

You should remember that this is a screening test. It does not say that your baby actually has these problems. It only says that you may be at increased risk for having them. If your test comes back abnormal we will have you see our counselor who will tell you exactly what your results mean.

Those people who may be at increased risk for neural tube defects will be offered an ultrasound first. This may determine that your dates are wrong, that your baby has a defect, or that everything looks normal. You will also be offerbed an amniocentesis (placement of a skinny needle through your abdomen into the uterine cavity to take out some of the fluid that is around the baby) to see if the alphafetoprotein is really elevated in the fluid. If we find a problem we will tell you more about it. If we don't find a problem we will simply watch your pregnancy more closely.

Those who are at risk for Down's Syndrome well be counseled about their chances of having an affected infant. They will be offered an amniocentesis to look at the baby's chromosomes. If they are normal you can be reassured and be followed in your pregnancy as usual. If they are abnormal you will be informed about what this means and what you can do next.

If you are over the age of 35 we will be offering you an amniocentesis anyway. You can speak with your counselor to see why you are at slightly greater risk for chromosome problems when you are 35 or older. You will still be offered the alphafetoprotein test, however, because this can still tell us about Neural Tube Defects.

Because this is a screening test not everyone who comes out "positive" will have a problem. Since we offer further studies to everyone who is positive there are some who will go through the process only to find out that the test was a "false positive". Some may elect not to have any further diagnostic procedures after the screening. Your pregnancy can be managed without screening. It is offered so that you can know more about your pregnancy and your risks for having one of the problems mentioned above. The provider who sees you for your obstetric visits will explain all of this to you and ask if you have any questions. Please feel free to ask about this at any time.